1. Field of the Invention
The present invention relates to a slip control apparatus and, more particularly, to an improvement in a slip control apparatus for a vehicle adapted to prevent a slip of the driven wheels with an improved stability in running.
2. Description of Related Art
Japanese Patent Publication (laid-open) No. 182,434/-1986, for example, discloses a slip control apparatus for a vehicle, as an automobile, which is designed such that a difference between velocities of the driven and undriven wheels of the vehicle is detected and the difference is adjusted so as to become a given value by subjecting output of an engine to feed-back control by means of a control over an opening degree of the throttle valve of the engine in order to adjust a velocity of the driven wheels, thus permitting an effective prevention of a slip of the driven wheels and improving a stability of running.
Other examples of subjecting the slip control of the vehicle to feed-back control are disclosed, for example, in U.S. Pat. No. 4,762,196 (counterpart of European Patent Application No. 87-110.079.8). U.S. Pat. No. 4,779,696 (counterpart of W. German Patent Application No. P 37 24 575.9), and U.S. Pat. Application Ser. No. 76,172 (counterpart of W. German Patent Application No. P 37 24 574.0).
The slip control apparatuses as have been described hereinabove are of the type in which output of the engine is subjected to the feed-back control to prevent a slip of the driven wheels so that, as a large degree of slip occurs, a reduction in the output from the engine is delayed requiring a longer time for regulating rotations of the driven wheels. Thus, there is a room for improvement in a rapid convergence of slip.
In order to solve the problems with a convergence of slip, it is considered that a feed-forward control is adopted in an initial stage of slip of the driven wheel in order to shorten a time required for a reduction in the engine output thus facilitating a convergence of slip in a shorter time. It is to be noted, however, that, if the feed-forward control is executed so as to reduce the engine output, a favorable convergence of slip of the driven wheels can be achieved so that, when the feed-back control starts thereafter, a convergence of the velocity of the driven wheel to a target value is delayed because the engine output is low, thus reducing a return responsiveness and providing no favorable acceleration.